Insulated conductor



Sept. 14, 1937. A, M, L 2,093,087

INSULATED CONDUCTOR Original Filed Nov. 21, 1928 lA/VE/VTOR CHM/06EACETATE ATTORNEY Patented Sept. 14, 1937 PATENT OFFICE mam-ran commc'roaAlger M. Lynn, OakParkJlL, muwm v Electric Company, Incorporated, NewYork, N. Y., a corporation of New York Original application November 21,1928, Serial Divided and this appllcation March 13, 1934, Serial No.715385 8 Claims- (Cl. INF-264) This invention relates to insulatedconductors and this application is a division of my copendingapplication Serial No. 320,794, filed November 21, 1928 issued as PatentNo. 1,966,509, dated July 17, 1934. a

Objects of the invention are to provide inexpensive insulating materialshaving high insulating properties, and which may be readily applied toelectrical conductors and to provide electrical l0 conductors havingthin, smooth, uniform and adherent coverings of eifective insulatingmaterials thereon.

In accomplishing the objects of the invention,

' one specific method embodying the invention 13 comprises serving afiat band of artificial silk filaments around a conductor to 'produce asmooth, uniform layer of the silk upon the conductor, and heating thecovered conductor to reduce the elasticity of the silk, so that it willhave little tendency to unravel.

The above enumerated and other objects and features of the inventionwill be apparent from the following detailed description of specificembodiments of the invention taken in connection with the accompanyingdrawing,'in which Fig. 1 is a fragmentary, longitudinal view of aconductor embodying the invention showing how the insulating material isapplied and having a part of the insulating material broken away to 80more clearly show the structure thereof;

Fig. 2 is a transverse sectional view thereof taken on line 2-2 of Fig.1; and

Fig. 3 is a sectional view of the insulating ma terial taken on line 3-3of Fig. 1.

Natural silk has been used heretofore as an insulating material forelectrical conductors, particularly for fine gauge wire such as magnetwire. In employing natural silk for this purpose it has been thepractice in some cases to use a fiat band 40 comprising four totwenty-five parallel ends of substantially untwisted twenty denierthreads composed of extremely fine individual filaments of one to threedenier. This band is frequently applied to the wire in a thin spirallayer. Although natural silk is an excellent insulator, it

is quite expensive, especially when used for insulating fine gauge wiresbecause very fine, continuous filament silk yarns are required for suchpurposes. The present invention contemplates the substitution of aspecially prepared artificial silk insulating material for natural silkand the application thereof to an electrical conductor in such mannerthat the conductor will be as effectively insulated as when natural silkis' employed and at a much lower cost,

In the manufacture of artificial silk the material from which the silkis made is extruded in the form of a liquid through dies, commonlycalled spinnerets, having a large number of minute holes therein throughwhich the 'material passes and from which the material emerges in 1 theform of extremely fine filaments, after which the filaments are passedthrough a suitable treating process, wherein the silk is solidified andconverted into its final form.. However, since artificial silk yarn ofthe usual type is of cylindrical cross-section and is composed of aplurality of individual filaments of the silk, it is difiicult toproduce a smooth, uniform insulating layer of such silk upon a conductorto form an insulator cover therefor. In practicing the present inventiona special type of artificial silk yarn is employed consisting of asingle band of individual filaments, wherein the filaments liesubstantially parallel to one another, and are so positioned that thefinished yarn will consist of a fiat, thin, comparatively wide bandwhich may be readily applied to a conductor to produce an exceptionallysmooth and uniform insulating covering for the conductor. Alsoartificial silk as usually produced in an economical manner at presentis considerably larger than the twenty denier yarn now employed in thenatural silk insulating bands. In the present invention asufficientnumber of individual fine filaments of artificial silk areextruded through a spinneret so as to produce a single fiat band ofeighty to five hundred deniers and comparable with the natural silkbands heretofore used for this purpose.

In the manufacture of artificial silks there are four commonly usedprocesses; namely,

1. Cellulose-acetate 2. Viscose 3. Cupra-ammonium 4. Nitro-cellulose Byemploying the cellulose-acetate process an artificial silk is producedwhich consists essentially of cellulose-acetate, which possessesinsulating properties comparable to those of natural silk, whereas bypracticing the other three processes enumerated above an artificial silkis produced which consists substantially of pure cellulose, whichpossesses insulating properties somewhat inferior to those of thecellulose acetate and natural silks. The differences in the insulatingproperties of these artificial silks necessitate the use of slightlydifferent procedures in the processes of insulating electricalconductors therewith, and various processes embodying the invention willnow be described.

' indicated by the numeral III in the accompanying drawing, and the thusformed band is served spirally around an electrical conductor l I, so asto form.therearound a thin, smooth, and substantially uniform coveringwhich comprises an efiective insulator for the conductor.

Since artificial silk is generally smooth and comparatively free frominterlocking fibres, and because it possesses comparatively highelasticity, it has a tendency to unravel from the cut end of a wireinsulated therewith, and this tendency is overcome in the case ofcellulose-acetatesilk by either one of two methods. The conductor, afterhaving been covered with the silk insulation, may be heated at amoderate controlled temperature to remove the natural strains in thesilk and possibly to slightly soften the celluloseacetate of which thesilk is composed, whereupon the elasticity of the silk is reduced andthe tendency of the silk insulation to unravel is there- 28 foresubstantially eliminated.

Electrical conductors, may also be insulated with satisfactory resultsby means of artificial silks made in accordance with the viscose,cupraammonium, nitro-cellulose or other processes in which the finishedsilk consists substantially of a regenerated cellulose only. when thesesilks are employed, they are served upon electrical conductors in theform of fiat, thin, comparatively wide bands in the same manner as hasbeen described hereinbefore in connection with the cellulose-acetatesilk, to form smooth, substantially uniform, helical coverings upon theconductors. The' insulated conductors are then treated with a lacquercomposed of cellulose- 40 acetatedissolved in acetone. which lacquerserves the double function of increasing the insulating properties ofthe silk insulation to a valuesubstantially equal to that of naturalsilk, and at the same timeactcsing as an adhesive to retain theinsulation in intimate contact with the conductor, so that theinsulation will not readily unravel.

It will thus be seen that the invention provides inexpensive insulatingmaterials having high in- 60 sulating properties, that insulatedconductors embodying the invention may be made therewith which'have verydesirable characteristics, and that such insulating materials may beeasily, cheaply and eifectively employed in practicing the as methodsembodying the invention to produce such conducto v a suitable solvent,such as Whatisclaimed is:

1. An insulated conductor, comprising a conductive'wire and asubstantially uniform covering therefor composed of a band of untwistedartificial filaments of a cellulose derivative helicallywrapped aroundsaid wire, said filaments being ununited and heat treated to removeinternal strains.

2. An insulated conductor, comprising a conductive wire and asubstantially uniform covering therefor composed of a band of untwistedand ununited artificial filaments of a cellulose ester helically wrappedaround said wire, said filaments being heat treated to remove internalstrains. v

3.- An insulated conductor comprising a conductive wire and asubstantially uniform covering therefor composed of artificial filamentsof a cellulose derivative wrapped around said wire, said filaments beingununited and heat treated to remove internal strains.

'4.A method of making insulated wire which comprises helically wrappinga band of u'ntwisted filaments .of a cellulose derivative around aconductive wire and heating the filaments below the coalescingtemperature of said cellulose derivative but sufiiciently toremoveinternai strains.

5. A method of making insulated wire which comprises wrapping a uniformcovering of artificial filaments of a cellulose derivative around aconductive wire, and heating said filaments below the coalescingtemperature of said cellulose derivative but sufficiently to removeinternal strains.

6. A method of making insulated wire which comprises helically wrappinga band of untwisted filaments of a cellulose ester around a conductivewire, and heating the filaments below the coalescing temperature of saidcellulose ester but sufiiciently to remove internal strains.

7. An insulated conductor, comprising a con- Amaa M. LYNN.

ductive wire and a substantially uniform cover-

